The Intellectual and Developmental Disabilities (IDD) Branch ofand Human Development NICHD sponsors research and research training aimed at preventing and ameliorating intellectual and developmental disabilities .This contract supports a mouse model of Down syndrome . The Repository of Mouse Models for Cytogenetic Disorders (Mouse Repository) began in the 1970s to generate and distribute mouse models for cytogenetic disorders, with special emphasis on Down syndrome (DS; trisomy 21). The creation of mouse models relevant to DS began in the 1970s and continued with the demonstration of genetic synteny between a segment of mouse chromosome 16 (Mmu16) and human chromosome 21 (Hsa21 ), which led to the use of the trisomy 16 mouse (Ts16) as a model for studies relevant to DS. Genes present on Hsa21 were localized to mouse chromosomes 17 and I 0 (Mmu17 and Mmu l 0) as well. Pattial trisomies for a number of syntenic chromosomal segments were generated in the 1980s, under contract to NICHD. One of these partial trisomies, designated Ts65Dn, proved to include approximately 150 genes located in what is considered the Down syndrome critical region of Hsa21. Subsequently, these mice were produced and distributed, under an NICHD contract, to investigators approved for receipt of them by NICHD. During the last 22 years, various investigators have generated other models relevant to DS. These include, but are not limited to, TslCje, Ts2Cje, TslRhr, MslRhr, Tel, and others. When these strains and stocks have been made available to the research community, the creation of a central repository has ensured their maintenance on appropriate genetic backgrounds and their distribution to investigators upon request in a timely manner and subsequent to approval by NICHD. Many of these mouse strains are maintained under cryopreservation. In 2010, the NICHD reissued the contract A Repository of Mouse Models of Cytogenetic Disorders with a substantial increase in investment to ensure timely access to and increased availability of mouse models for cytogenetic disorders, particularly Ts65Dn, to the research community, and to ensure increased experimental efforts to modify the existing genetic backgrounds for the various strains to increase availability and ease of use by investigators. A substantial number of responses identified the need for increased availability of the mouse models to the research community as a priority issue.